1. Field of the Invention
The present invention relates to the field of atomic spectroscopy, and more particularly to a unique temperature controller for sensing and regulating the evaporation and condensation rate of a metallic liquid inside a closed vapor cell comprising an atomic optical filter.
2. Description of the Prior Art
Closed vapor cells filled with metallic vapor at a particular pressure exhibit sharply defined line spectra when excited by external stimuli such as an electrical current or light from a suitable source. This principle is used in the lighting field for sodium and mercury vapor lamps. Vapor cells are also used for atomic spectroscopy, and more particularly in resonant laser absorption spectroscopy. However, such applications require tightly controlled pressures and temperatures for predictable and repeatable results. To maintain the internal vapor pressure at a predetermined fixed level, a reservoir, called a "cold spot" containing a metal alkali in a liquid state, is used. At some localized point within or near the main chamber of the vapor cell, this open reservoir is held at a constant temperature less than that of the cell itself hence the name "cold spot"). The reservoir maintains a constant gas pressure of the metallic vapor inside the cell and provides a condensation point that constant at a value below the temperature of the cell so as to provide the desired "cold spot" for the cell.